This is the stuff I work with, it's a semiconductor crystal called cadmium zinc telluride (CZT) that is REALLY good at measuring photon-based radiation (X-rays and gamma-Rays).
The current gold-standard is a semiconductor radiation detector called a High-Purity Germanium detector (HPGe) tha can achieve 0.20% energy resolution from the Cesium-137 662 keV gamma-ray photopeak. All you need to know from that is that Cesium-137 emits a gamma ray that ALWAYS has 662 keV energy, and the histogram of energy measurements from HPGes will usually measure that energy accurately. The problem with HPGes is that they can only be operated when they're cryogenically cooled to 77K (room temperature is 293K, for reference), and this cooling takes HOURS to do.
CZT on the other hand does not require this cooling as a result of material properties and has recently achieved 0.31% energy resolution from the aforementioned 662 keV peak from Cesium-137. This is really cool sine it means that you can get very close to gold-standard energy spectroscopy after only about 5-10 minutes of properly starting a detector that uses CZT.
And what can you use this for? Think about where you might want to identify very specific radioactive sources in a short period of time. Or think about where it might be useful to measure what x-rays might scatter off of (collide with an atom and change its momentum like billiard balls hitting each other, for example). I won't go into applications here, but suffice to say, this crystal has been dominating my life for almost two years now, and I anticipate it staying in my life for years to come.